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Suddenly a common sight on cycleways, the e-bike is not confined to cities; e-mountainbikes are available to ease trail riders' journeys back up the hill.

As yet a small part of the cycle market, e-bikes are fast gaining popularity. With 2327 imported last year, they were 1 per cent of all bike imports, but this marked a near four-fold increase since 2012. Retailers report sales growth of 35 per cent a year.

Importer and retailer Neil Pollett, owner of Flux, in Ponsonby, says the "grey-power" age group were first to embrace e-bikes, but the trend had caught on with people in their 30s to 50s, and even younger.

"I get students who want to get to university - there's no car parking at university."

Mr Pollett says the attraction, as well as free parking, is that e-bikes overcome the difficulty of pedalling up Auckland's many hills, riders don't get sweaty, don't need to shower at work and don't need to wear special clothes.

New Zealand Post has 280 e-bikes and 25 more on order, a spokeswoman said. "The New Lynn, Rotorua, Kapiti and Timaru branches are all using e-bikes, plus we have a sprinkling of others around the country. The e-bikes are good on hills and on the flat.

"The e-bikes are popular with our posties as they have a lot of health benefits. They are easier on the knees and posties generally feel fresher and less tired at the end of their round."

Mayor Brown's office has two e-bikes, which it says are used by him and his staff.

Auckland Transport says e-bikes have contributed to cycling's growth in the city. The number of people cycling on the Grafton Gully Cycleway last month was 33 per cent greater than in March last year.

The agency helps businesses to run trials of adding e-bikes to their fleet, and also has four of its own.

"Auckland Transport has three e-bikes that all staff can use to get to and from meetings," a spokesman said. "These have proved hugely popular, with one of the bikes clocking up close to 2000km since it was bought in spring last year."